The present disclosure relates to a semiconductor structure and a method of fabricating the same. More particularly, the present disclosure relates to a p-channel field effect transistor (pFET) device including a silicon germanium (SiGe) channel in which the junction profile of the source region and the drain region is abrupt. The present disclosure also relates to a method of fabricating such a pFET device.
The development of Si/SiGe heterostructure metal oxide semiconductor field effect transistors (MOSFETs) has been encouraged by their potentially higher carrier mobility, low cost and ease of integrating into current MOSFET processing flows. Compressively strained SiGe grown epitaxially on Si substrates can be used to create a two-dimensional hole channel, which has a lower effective mass thereby contributing to an enhanced mobility. By selective band-gap engineering, pseudomorphic SiGe channel pMOSFETs can be produced which provide a superior alternative to the lower hole mobility of conventional Si pMOSFETs.
One problem with conventional SiGe channel pMOSFETs is that a p-type dopant such as boron used in forming the source region and the drain region diffuses much slower in SiGe than Si. As such, the junction of the source region and the drain region in the underlying Si area encroaches more and is deeper for a given amount of junction/gate overlap than in a conventional Si MOSFET thereby degrading short channel effects.
A potential solution to this problem is to grow an extremely thick SiGe channel atop a Si substrate. Such a solution is however not feasible since an increased number of mis-fit dislocation defects will form in the SiGe layer which, in turn, will degrade the performance of the pMOSFET device.